Synthesis, optical properties, crystal structures and phase behaviour of selectively fluorinated 1,4-bis(4′-pyridylethynyl)benzenes, 4-(phenylethynyl)pyridines and 9,10-bis(4′-pyridylethynyl)-anthracene, and a Zn(NO3)2 coordination polymer

Article abstract of DOI:10.1039/b405128a

A series of selectively fluorinated and non-fluorinated rigid rods based on the 4-pyridylethynyl group, namely 1,4-bis(4′-pyridylethynyl)benzene (1a), 1,4-bis(4′-pyridylethynyl)tetrafluorobenzene (1b), 1,4-bis(2′,3′,5′,6′-tetrafluoropyridylethynyl)benzene (1c), 1,4-bis(2′,3′,5′,6′-tetrafluoropyridylethynyl) tetrafluorobenzene (1d), 9,10-bis(4′-pyridylethynyl)anthracene (2), 4-(pentafluorophenylethynyl)pyridine (3a) and 4-(phenylethynyl)- tetrafluoropyridine (3b) were prepared in good yields using Pd/Cu-catalysed Sonogashira cross-coupling reactions and/or lithium chemistry involving nucleophilic aromatic substitution. UV-Vis absorption and fluorescence spectra for 1a-d and 2 are reported. The X-ray crystal structures of 1b, 1c, 2, 3a and 3b show a variety of packing motifs, none of which involve arene-perfluoroarene stacking. The phase behaviour of 1a-1c has been studied by differential thermal analysis and transmitted polarised light microscopy. Compound 1b exhibits an ordered phase between 227.6 and 272.5 °C which is either hexatic B or crystal B. A 1:1 complex (4) between 1b and Zn(NO₃)₂ has been prepared; its crystal structure consists of zig-zag polymer chains held together by hydrogen bonds.

Full text of DOI:10.1039/b405128a

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A R T I C L E
Synthesis, optical properties, crystal structures and phase behaviour
of selectively fluorinated 1,4-bis(4’-pyridylethynyl)benzenes,
-(phenylethynyl)pyridines and 9,10-bis(4’-pyridylethynyl)-
anthracene, and a Zn(NO ) coordination polymer
4
3
2
a,b,c
a
Jonathan C. Collings, Donocadh P. Lydon,
a
Tolulope M. Fasina,*
a
a
a
David Albesa-Jove, Andrei S. Batsanov, Judith A. K. Howard, Paul Nguyen,
b
b
d
d
e
Mitch Bruce, Andrew J. Scott, William Clegg, Stephen W. Watt, {
Christopher Viney { and Todd B. Marder*
e
a,b
a
Department of Chemistry, University of Durham, South Road, Durham, UK DH1 3LE.
E-mail: Todd.Marder@durham.ac.uk
b
Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
Department of Chemistry, University of Lagos, Lagos, Nigeria
c
d
School of Natural Sciences (Chemistry), University of Newcastle upon Tyne, Newcastle
upon Tyne, UK NE1 7RU
e
Department of Chemistry, School of Engineering and Physical Sciences, Heriot-Watt
University, Riccarton, Edinburgh, UK EH14 4AS
Received 6th April 2004, Accepted 4th May 2004
First published as an Advance Article on the web 28th May 2004
A series of selectively fluorinated and non-fluorinated rigid rods based on the 4-pyridylethynyl group, namely
1
,4-bis(4’-pyridylethynyl)benzene (1a), 1,4-bis(4’-pyridylethynyl)tetrafluorobenzene (1b), 1,4-bis(2’,3’,5’,6’-
tetrafluoropyridylethynyl)benzene (1c), 1,4-bis(2’,3’,5’,6’-tetrafluoropyridylethynyl)tetrafluorobenzene (1d),
,10-bis(4’-pyridylethynyl)anthracene (2), 4-(pentafluorophenylethynyl)pyridine (3a) and 4-(phenylethynyl)-
9
tetrafluoropyridine (3b) were prepared in good yields using Pd/Cu-catalysed Sonogashira cross-coupling
reactions and/or lithium chemistry involving nucleophilic aromatic substitution. UV-Vis absorption and
fluorescence spectra for 1a–d and 2 are reported. The X-ray crystal structures of 1b, 1c, 2, 3a and 3b show a
variety of packing motifs, none of which involve arene–perfluoroarene stacking. The phase behaviour of 1a–1c
has been studied by differential thermal analysis and transmitted polarised light microscopy. Compound 1b
exhibits an ordered phase between 227.6 and 272.5 uC which is either hexatic B or crystal B. A 1 : 1 complex
3 2
(4) between 1b and Zn(NO ) has been prepared; its crystal structure consists of zig-zag polymer chains held
together by hydrogen bonds.
The nature of the bridging ligand plays an important role in
Introduction
manipulating the overall structure of the coordination network
and in the recognition ability of a system, which depends on the
nature of the cavity. Fluorination of the aromatic ligand can
lead to specific recognition of electron-rich arene compounds,
There has been intense activity in the area of supramolecular
1
self-assembly within the last decade. Metal–ligand coordina-
tion has proved useful in the assembly of functional molecular
2
materials which include a variety of one-dimensional chains,
two-dimensional sheets and three-dimensional networks con-
9
and can favour clathrate formation over interpenetration.
This prompted us to synthesise a series of fluorinated
(4-pyridylethynyl)benzene-based rigid rods for use in self-
assembly. Several ortho-ethynyl-substituted fluorinated pyri-
3
taining cavities of various sizes. The goal is the design and
assembly of structures with potential applications as catalytic,
luminescent, and magnetic materials, and porous structures for
use in separations.
N,N’-Bridging ligands built from two 4-pyridyl units have
been widely utilised in the construction of these structures.
Although 4,4’-bipyridyl has been employed extensively as a
bridging ligand in networks with a high degree of porosity,
several groups have reported the use of longer bis(4-pyridyl)
1
0
dine derivatives have been prepared previously. In this paper,
we report the synthesis of a series of fluorinated 1,4-bis(4’-
pyridylethynyl)benzenes, 1,4-bis(4’-pyridylethynyl)anthracene,
and 4-(pentafluorophenylethynyl)pyridine by Sonogashira
cross-coupling. We also report the synthesis of 4-(phenylethy-
nyl)tetrafluoropyridine via nucleophilic substitution on penta-
fluoropyridine by lithium phenylacetylide, and the preparation
and crystal structure of a 1 : 1 coordination polymer of 1,4-
bis(4’-pyridylethynyl)tetrafluorobenzene with zinc(II) nitrate.
4
5
6
units of the type Py–X–Py (Py ~ 4-pyridyl; X ~ CH
2
CH
, CMC–C
2
,
CHLCH, CMC, CMC–CMC, C
6
4
H , C14
H
8
, C H –
6 4
6
F
4
7
CMC) as ligands. Fujita recently reported the use of a longer
bis(4’-pyridyl)-p-p-p-triphenylene ligand in the construction of
8
Results and discussion
˚
a 24 6 24 A square ladder.
Synthesis
{
Present address for S. W. W.: Department of Chemistry, University
of Cambridge, Lensfield Road, Cambridge, UK, CB2 1EW.
Present address for C. V.: School of Engineering, University of
California at Merced, P.O. Box 2039, Merced, CA 95344, USA.
Most of these compounds were prepared using the Sonogashira
Pd/Cu-catalysed cross-coupling reaction, an efficient method of
synthesizing aryl and heteroaryl alkynes in good yields via the
{
T h i s j o u r n a l i s ß T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 3 9 5 – 2 4 0 4
2 3 9 5

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Scheme 1 Synthesis of 1,4-bis(4’-pyridylethynyl)benzenes (1a–d).
coupling of aryl halides with terminal alkynes, with aryl iodides
in much lower yield, from the di-lithiation of 1,4-diethynyl-
benzene followed by quenching with two equivalents of
pentafluoropyridine. Compound 1d could only be isolated in
20% yield from Sonogashira reactions, and was shown by
EI mass spectrometry to contain traces of the butadiyne
1
1
being more reactive than corresponding bromides. Two
compounds were synthesised by nucleophilic aromatic sub-
stitution by lithium acetylides on pentafluoropyridine. Similar
substitution reactions on highly fluorinated arenes have been
1
2
reported.
The synthesis of the 1,4-bis(4’-pyridylethynyl)benzenes
1a–d) is shown in Scheme 1. Compounds 1a and 1b contain
derivative C
which have been shown
5
F
4
N–CMC–C
6
F
4
–CMC–CMC–C
6
F
4
–CMC–C
5 4
F N,
1
3a
to result from hydrodehalogena-
(
tion pathways during Sonogashira reactions with highly
fluorinated systems, as well as an unidentified species with a
peak at m/e ~ 530.
unfluorinated pyridyl rings and were prepared by coupling two
equivalents of 4-ethynylpyridine with 1,4-diiodobenzene
and 1,4-diiodotetrafluorobenzene respectively. The coupling
to form 1a occurred in two hours at room temperature in
diisopropylamine; however, 1b required four hours reflux in
triethylamine. In contrast, compounds 1c and 1d containing
fluorinated pyridyl rings were prepared via the coupling of two
equivalents of 4-bromotetrafluoropyridine with 1,4-diethynyl-
benzene or 1,4-diethynyltetrafluorobenzene, respectively in
refluxing triethylamine. We, and subsequently several other
The synthesis of 9,10-bis(4’-pyridylethynyl)anthracene (2) via
Sonogashira coupling is shown in Scheme 2. Two alternative
syntheses were employed; in the first, two equivalents of
4-ethynylpyridine were coupled with 9,10-diiodoanthracene in
diisopropylamine at room temperature, using the well-known
catalyst precursor Pd(PPh ) Cl . In the second method,
3
2
2
4-ethynylpyridine was coupled to the less reactive, but com-
mercially available, 9,10-dibromoanthracene in triethylamine
at room temperature, using a more active catalyst system
1
3
groups, have reported the synthesis of the parent compound
a as a yellow–orange powder with yields ranging from 15 to
9%. In the present study, 1a was obtained in 60% yield as a
t
14
1
9
prepared in situ from Pd(PhCN)
Cl
2 2
1 2P Bu
3
.
Column
chromatography on basic alumina using hexane/ethyl acetate
afforded the desired compound which was judged pure by
NMR spectroscopy and EI MS. However, in spite of repeated
attempts, on a variety of samples, a satisfactory elemental
analysis could not be obtained. As the analyses were always
rather low in carbon, it appears that this may be the result of
incomplete combustion.
white powder after column chromatography on basic alumina
using hot toluene as the eluent. Thus, it seems likely that the
yellow–orange colour observed previously was due either to a
trace impurity or to the presence of a coloured polymorph.
Compounds 1b and 1c were worked-up analogously in com-
parable yields. We have also prepared compound 1c, although
3 2 2 2 2
Scheme 2 Synthesis of 9,10-bis(4’-pyridylethynyl)anthracene (2) (for X ~ I, Pd cat. ~ Pd(PPh ) Cl ; for X ~ Br, Pd cat. ~ Pd(PhCN) Cl /2
t
P Bu
3
).
2
3 9 6
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 3 9 5 – 2 4 0 4

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Scheme 3 Synthesis of (4-pyridylethynyl)benzenes (3a–b).
The compound 4-(pentafluorophenylethynyl)pyridine (3a)
was obtained in moderate yield via the coupling of one
equivalent of 4-ethynylpyridine with iodopentafluorobenzene
in refluxing triethylamine. In contrast, 4-(phenylethynyl)tetra-
fluoropyridine (3b) was synthesised in high yield via aromatic
nucleophilic substitution of pentafluoropyridine by lithium
phenylacetylide at 278 uC in dry THF, with substitution taking
the change in absorption wavelength being larger for the non-
fluorinated compounds 1a and 2. The emission wavelength of
2 is red shifted from 574 to 634 nm and the solution changes
colour from fluorescent green to orange.
Crystal structures
1
2
The molecular structures of 1b, 1c, 2, 3a and 3b, determined by
single-crystal X-ray diffraction, are shown in Fig. 1. Molecules
place exclusively at the para-position. Column chromato-
graphy on silica, eluting with hexane, gave a high yield of
analytically pure product. This compound has been reported
previously from the reaction of trimethylsilylethynylbenzene
with pentafluoropyridine in the presence of KF in DMF at
1
3
b and 1c have crystallographic inversion centres, while 3a and
b have no crystallographically imposed molecular symmetry.
All four molecules adopt nearly planar conformations, with the
dihedral angles t between the benzene and the pyridine rings
being 2.5, 5.6, 0.4 and 3.4u, respectively. Molecule 2 lies on a
crystallographic twofold axis, passing through the atoms N(1),
C(3), C(4), C(5), C(6), C(13), C(14), C(15), C(16) and N(2). The
two pyridine rings of the molecule have different orientations,
rotated by 5.0 and 64.8u with respect to the anthracene plane.
As shown in Table 2, N–C bonds in fluorinated pyridine rings
are significantly shortened, and the single C–C bonds between
the acetylene and arene groups are marginally shorter when
the latter is fluorinated. Both effects can be explained by the
polarity of these bonds being diminished or reversed by the
induction effect of fluorine substituents.
Complex 4 has a polymeric (catena) structure (Fig. 2). The
zinc atom lies on a twofold axis and has a distorted tetrahedral
2 2
N O coordination with two 1b ligands (whose planes are
almost perpendicular) and two monodentate nitrate anions.
Thus, the structure contains an infinite zig-zag chain –1b–Zn–
¯
1b–Zn–, running parallel to the [2 0 1] direction. The bridging
1
5
room temperature. These reactions are shown in Scheme 3.
Careful layering of an ethanol solution of Zn(NO ) ?6H O
3
2
2
2 2
over a CH Cl solution of 1b led to the deposition of a fine
precipitate and the slow growth, at the layer interface, of light-
yellow crystals of the coordination polymer, 4. Polymer 4
contains no water, as the Zn(II) coordination environment is
essentially tetrahedral, with two bound pyridyl nitrogens and
two monodentate NO ligands, vide infra.
3
Luminescence
As these compounds are analogues of 1,4-bis(phenylethynyl)-
1
3a
11c
benzenes
and 9,10-bis(phenylethynyl)anthracenes
which
are highly luminescent, we investigated their UV-vis absorption
and emission spectra, which are summarised in Table 1. The
bis(4-ethynylpyridyl)benzene compounds 1a–d all absorb in the
region 314–320 nm with the extinction coefficient increasing
as the degree of fluorination increases. Fluorination of the
compounds leads to the presence of a shoulder near 333 nm in
compounds 1b and 1c, but a distinct sharp peak at 336 nm was
observed in the fully fluorinated compound 1d, which, in the
latter case, could be a result of impurities (vide supra). There is a
larger variation in their emission maxima with fluorination,
compared to their absorption spectra. Expectedly, compound 2
absorbs at a longer wavelength of 436 nm as a result of
increased conjugation in the anthracene. This compound is
highly emissive, at 574 nm, which makes it suitable for use as a
fluorescent chromophore.
1b ligand has crystallographic inversion symmetry and a nearly
planar conformation (t ~ 6.1u). The changes in bond distances
compared to those in the crystal structure of pure 1b are within
3 e.s.d.’s, although they are not inconsistent with an increased
conjugation along the rod. Similar polymeric structures have
1
6
been found in a series of (4,4’-bipyridine)ZnX
2
complexes,
16c
S, salicy-
1
6a
16b i
SPh, SP(OPr )
where X ~ S COCH
16e
late, or SCOPh.
2
2
CHMe
2
,
2
1
6d
Crystal packing of the compounds is basically of two
different modes. The structure of 1b is composed of flat layers
of molecules (Fig. 3), approximately parallel to the lattice plane
(1 0 3). The long axes of molecules throughout the structure
form two parallel sets with an 81u angle between them. Of the
Protonation of the compounds in solution by addition of
trifluoroacetic acid results in a bathochromic shift in the UV-
vis absorption and emission spectra of all of the compounds,
Table 1 Absorption and luminescence data in acetonitrile
a
a
Compound
lmax/nm
log e
lmax (emission)/nm
l
max /nm
lmax (emission) /nm
1
1
1
1
2
a
a
b
c
315
314
320
3.33
3.98
4.33
4.65
402
362
446
366
336
338
424
486
473
b
d
316, 336(sh)
436, 462
4.21, 4.24
574
510
634
b
After addition of trifluoracetic acid. The shoulder in the absorption spectrum may be due to impurities; the emission spectrum is not
reported, as the impurities are likely to be highly luminescent; see text.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 3 9 5 – 2 4 0 4
2 3 9 7

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Fig. 1 Molecular structures of 1b, 1c, 2, 3a and 3b, projected on the plane of the central rings and showing 50% displacement ellipsoids. Atoms
generated by inversion centres (1b, 1c) or twofold axis (2) are primed.
˚
Table 2 Selected bond distances (average) in A
Bond
1b
1c
2
3a
3b
4
i
ii
iii
iv
v
1.338(2)
1.385(2)
1.395(2)
1.435(2)
1.193(2)
1.424(2)
1.310(4)
1.381(4)
1.390(4)
1.423(3)
1.199(4)
1.432(3)
1.332(2)
1.384(2)
1.394(1)
1.433(2)
1.198(2)
1.430(2)
1.342(3)
1.374(3)
1.395(3)
1.427(3)
1.199(3)
1.414(3)
1.305(2)
1.383(2)
1.393(2)
1.426(2)
1.196(3)
1.438(2)
1.347(2)
1.380(2)
1.397(2)
1.427(2)
1.199(2)
1.414(2)
vi
˚
four symmetry-independent H atoms, one is involved in a
…
one F atom at 2.48 A. In its packing motif, and in the lattice
parameters, 3a can be described as a distorted (sheared)
analogue of the structures of C F CMCPh or of the 1 : 1 com-
…
C(3)–H N(1) hydrogen bond and the rest in H F contacts
…
with other molecules of the same layer. The H N distance§ of
˚
.34 A is significantly shorter than the sum of van der Waals
6
5
1
8a
2
radii of 2.74 A, while H F distances (2.51–2.52 A) are close to
plex between PhCMCPh and C F CMCC F . The two latter
structures are dominated by stacks of alternating phenyl and
pentafluorophenyl rings, as are the structures of pentafluoro-
6
5
6 5
˚
…
˚
1
7
˚
the corresponding sum (2.56 A). Adjacent layers are offset
to such an extent that there is practically no stacking interac-
tion between aromatic rings. The shortest interlayer contact,
1
8b
18c
stilbene,
pentafluorodiphenylbutadiyne
partially fluori-
and other related
However, in 3a, the offset is much larger, so
that the Py and C F rings overlap either by a single atom [C(5)
1
8d,e
nated bis(phenylethynyl)benzenes
˚
between C(6) and C(11), is 3.35 A.
A layered motif is also adopted by 3a; in this triclinic
structure, all molecules are mutually parallel/antiparallel
18f–k
systems.
6
5
eclipsed with C(9), at a 3.33 A˚ distance], or not at all.
(Fig. 3). The intermolecular but intra-layer contacts between
hydrogens and negatively charged atoms are longer than in 1b,
but more numerous. Thus, H(1) and H(2) contact two F
In contrast, the structures of 1c and 3b are composed of
infinite stacks of molecules (Fig. 4). Adjacent molecules in a
stack are related by a translation (b in 1c, a in 3b) and are
therefore strictly parallel but are offset in the direction of their
long axes, so that both the benzene and the pyridine rings
overlap with CMC bonds (Fig. 5). The mean interplanar
…
atoms each (H F 2.61–2.69 A), H(5) contacts one F and one
˚
˚
N atoms at 2.60 and 2.45 A respectively, while H(4) contacts
˚ ˚
separations are 3.41 A in 1c and 3.35 A in 3b. The stacks are
˚
§ An idealized C–H distance of 1.08 A was used for all calculations of
hydrogen contacts.
1
arranged in a c, or flattened herringbone pattern, so that the
9
2
3 9 8
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 3 9 5 – 2 4 0 4

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Fig. 2 Part of the polymeric structure 4. Atoms generated by an
inversion centre are primed, those generated by a twofold axis are
double-primed. Important bond distances and angles within the
˚
organic ligand are provided in Table 2. Selected bond distances (A)
and angles (u) in the coordination sphere of Zn are: Zn–O(1) ~
1.9918(13), Zn–N(1) ~ 2.0267(13), N(1)–O(1) ~ 1.296(2), N(1)–
O(2) ~ 1.222(2), N(1)–O(3) ~ 1.242(2); O(1)–Zn–O(1’) ~ 88.24(8),
N(1)–Zn–N(1’) ~ 109.19(8).
Fig. 4 Crystal packing of 1c and 3b (H atoms are omitted for clarity).
Fig. 5 Overlap of adjacent molecules in a stack of 1c.
fifth H atom forms none. In both structures these contacts are
…
slightly longer than in 1b, and N H contacts are rendered
impossible.
In the structure of 2, the nearly-planar parts of the molecules
are stacked in a head-to-tail fashion, so that the anthracene
moiety overlaps with the almost parallel pyridine ring while the
rotated pyridine rings lie between the stacks. The mean
˚
interplanar separation in a stack is 3.40 A and the shortest
…
˚
intermolecular contact C(3) C(7) is 3.41 A. As in the crystal
structures of 1c and 3b, the pyridine nitrogen atoms of 2 do not
accept any hydrogen bonds.
Fig. 3 Crystal packing of 1b and 3a, showing intermolecular hydrogen
…
bonds C–H N.
The packing motif of 4 can be described as a layer of zig-zag
chains (related by the b translation), followed by an antiparallel
layer (Figs. 6 and 7). The apparent resemblance to the packing
motif of 1c, however, is deceptive; adjacent 1b-ligands in 4 have
a large lateral offset and no overlap between the rings, rather
like in the structures of 1b and 3a. Of the four independent H
atoms, one is engaged in a relatively strong intra-chain
molecules in adjacent stacks form a dihedral angle of 84.5u (1c)
and 84.6u (3b) and have a close contact through their N atoms,
…
… …
˚ ˚
N chain (N N 3.21 A in 1c, 3.24 A
forming a zig-zag N
N
in 3b). In the structure of 1c, the stacks form a continuous
herringbone layer; in 3b there are only two-stack herringbone
arrays, with the ‘‘arrows’’ directed in both a and 2a directions,
as well as those differing by a 90u pseudo-rotation around this
axis (Fig. 4). The two independent H atoms in the structure 1c
…
…
˚
hydrogen bond C(2)–H O(3) (H O 2.30 A, cf. the sum of
1
van der Waals radii of 2.68 A) and the rest in inter-chain
7
˚
…
˚
form two H F contacts each (2.55–2.74 A), whilst in 3b four
…
interactions, two with O atoms (H O 2.39 and 2.45 A) and
˚
˚
H atoms form one to three contacts each (2.56–2.79 A) and the
…
˚
one with F (H F 2.41 A).
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 3 9 5 – 2 4 0 4
2 3 9 9

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Table 3 Phase behaviour data for compounds 1a–d and 2
a
b
Compound
Mp /uC
Transitions upon heating
K 192.3 I
K 227.6 hexatic B/crystal B 272.5 deg
1
1
1
1
2
a
a
b
c
192–193
235
dec
c
dec
247
166
233
K 313.9 I/deg
dec
d
N/A
N/A
dec
dec
Meltemp II apparatus, uncorrected;
slow heating. From DTA experiments. Transition temperatures
from tplm; see text.
~ decomposition noted on
b
c
behaviour. Thus, a mesophase appeared at 227.6 uC (estimated
from tplm) upon heating, which persisted until the sample
degraded at 273.5 uC. The optical texture of this phase as
observed by tplm, and shown in Fig. 8, is consistent with either
hexatic B or crystal B. Whilst distortion under stress points to
crystal B, rounded edges of the domains are suggestive of the
possibility of the more fluid hexatic B phase. A definitive
assignment of the phase requires X-ray diffraction studies at
high temperature, perhaps in the presence of an aligning
magnetic field, and such experiments are planned. Suffice it to
say at this time that a new hexagonal phase is observed at
higher temperatures which is clearly distinct from the one in the
single-crystal X-ray structure.
Fig. 6 Crystal packing of 4 (H atoms are omitted).
Thus, neither phenyl and tetrafluoropyridyl, nor pyridyl and
pentafluorophenyl moieties form the mixed-stack motif, which is
20
typical for arene–perfluoroarene complexes and is also observed
in the structures of the related compounds 4-biphenyl-tetrafluoro-
pyridine, 2,4,6-trimethylphenylazo-tetrafluoropyridine and 2,4,6-
Conclusion
Sonogashira palladium/copper-catalysed cross-coupling reac-
tions provide a practical synthetic route to several selectively
fluorinated rigid rods containing the 4-pyridylethynyl group,
whereas others were prepared via lithium chemistry. These
compounds are highly luminescent. Several of their crystal
structures have been solved from X-ray diffraction data which
show the molecules to be arranged in a variety of packing
motifs. The compound 1,4-bis(4’-pyridylethynyl)tetrafluoro-
benzene has been shown by differential thermal analysis and
transmitted polarised light microscopy to exhibit, at high
temperature, a hexagonal phase which could be either a hexatic
B mesophase or a crystal B phase. High-temperature X-ray
diffraction studies are required to establish which is the case. In
addition, a 1 : 1 coordination polymer of 1,4-bis(4’-pyridyl-
21
trimethylphenylazoxytetrafluoro-pyridine.
Phase behaviour
In a melting point capillary, in air, only 1a showed a clean
melting point of 192–193 uC. Slow heating of the other com-
pounds led to decomposition as indicated in Table 3. Given the
rigid-rod shape of these systems, the phase behaviour of
compounds 1a, 1b and 1c was studied in more detail using
differential thermal analysis (dta) and transmitted polarised
light microscopy (tplm). The phase transition data are also
given in Table 3. Only 1b was found to exhibit mesomorphic
ethynyl)tetrafluorobenzene with zinc(II
) nitrate has been
obtained in which the ligands are arranged in infinite zig-zag
chains linked by the metal centres. Future work will con-
centrate on obtaining the crystal structures and evaluating the
properties of new coordination polymers from these ligands in
combination with other metal salts.
Fig. 8 The texture of the crystal B or hexatic B phase of 1b viewed by
transmitted polarised light microscopy. Image shows 50.33 mm by
33.66 mm region of sample.
Fig. 7 Overlap of adjacent molecules in a stack of 4, also showing the
hydrogen bonding between the stacks.
2
4 0 0
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 3 9 5 – 2 4 0 4

View Article Online
of 1,4-diethynylbenzene (0.19 g, 1.50 mmol), PdCl (PPh )
3 2
Experimental
2
(
0.421 g, 0.060 mmol) and CuI (0.011 g, 0.060 mmol) in
All reactions were performed under an atmosphere of dry
nitrogen using standard Schlenk techniques. The solvents
diethylamine, diisopropylamine and triethylamine were freshly
triethylamine (30 mL). The reaction mixture was heated to
reflux for 3 h after which the solvent was removed in vacuo. The
residue was dissolved in hot toluene and eluted through a
column of alumina (4 cm). Cooling of the toluene solution gave
distilled from CaH under nitrogen prior to use. NMR spectra
2
1
were recorded on a Varian Mercury 200 MHz spectrometer
1
the desired compound as a yellow solid. Yield 0.49 g (77%). H
1
19
1
1
9
operating at 200 MHz for H and 188 MHz for F{ H}.
Proton chemical shifts are relative to TMS and referenced
NMR (200 MHz ) d: 7.66 (4H, s, ArH). F{ H} NMR
(188 MHz) d: 290.4 (4F, m, PyF), 2138.3 (4F, m, PyF).
1
9
2
1
against residual CHCl
shifts are referenced to external CFCl
3
as the internal standard; F chemical
. Chemical shifts are
20 4 8 2
IR/cm : 2227. MS (M1): m/z 424. Anal. calc. for C H F N :
3
C 56.62, H 0.95, N 6.60. Found: C 56.80, H 0.90, N 6.44%.
reported in ppm and coupling constants in Hz. FT-IR spectra
were recorded from Nujol mulls on a Perkin-Elmer 1600 FT-IR
spectrophotometer. Absorption spectra were recorded on a
Hewlett-Packard 8453 diode array UV-vis spectrophotometer
in acetonitrile. Fluoresence spectra were measured on a Jobin-
Yvon Fluoromax 3 spectrophotometer in acetonitrile. Ele-
mental analyses were obtained from M-H-W Laboratories,
Phoenix, Arizona and the University of Durham elemental
analysis service. GC/MS analyses were performed on a
Hewlett-Packard 5890 Series II gas chromatograph equipped
with a 5971A mass selective detector and a fused silica capillary
column. The following operating conditions were used: injector
Alternative synthesis of 1,4-(4’-pyridylethynyl)tetrafluoro-
benzene (1c)
A solution of n-butyllithium in hexane (1.6 M, 6.25 mL,
0.0 mmol) was added dropwise to a solution of 1,4-
1
diethynylbenzene (0.63 g, 5.0 mmol) in dry THF at 278 uC,
and the reaction was stirred for 1 h. Pentafluoropyridine (1.69 g,
1
0.0 mmol) was added at 278 uC, and the solution was allowed
to warm to room temperature and stirred for 16 h. The solvent
was evaporated and the residue was filtered through a column
of silica (4 cm) using hot toluene. The product crystallised as
yellow needles upon cooling. Yield 0.85 g (34%).
2
50 uC; detector 280 uC; oven temperature was ramped from 70
21
to 280 uC at a rate of 20 uC min . UHP grade helium was used
as the carrier gas. High resolution EI-MS was performed on a
Micromass Autospec mass spectrometer. High resolution
electrospray ionisation (ESI) mass spectrometry was performed
on a Micromass LCT spectrometer running in high resolution
Synthesis of 1,4-bis(2’,3’,5’,6’-tetrafluoropyridylethynyl)-
tetrafluorobenzene (1d)
A solution of 4-bromo-2,3,5,6-tetrafluoropyridine (0.45 g,
2.00 mmol) in triethylamine (20 mL) was added to a suspen-
sion of 1,4-diethynyltetrafluorobenzene (0.17 g, 0.90 mmol),
2
2
ES1 mode. The compound 9,10-diiodoanthracene and the
2
3
terminal alkynes 4-ethynylpyridine,
1,4-diethynylbenzene
2
4
PdCl
0
2 3 2
(PPh ) (0.026 g, 0.037 mmol) and CuI (0.007 g,
.037 mmol) in triethylamine (30 mL). The reaction mixture
and 1,4-diethynyltetrafluorobenzene were prepared by litera-
ture procedures, and all other reagents were obtained from
commercial sources and used as received.
was heated to reflux for 12 h after which the solvent was
removed in vacuo. The residue was dissolved in hot toluene and
eluted through a column of alumina (4 cm) with DCM/toluene.
Synthesis of 1,4-bis(4’-pyridylethynyl)benzene (1a)
19
1
Yield 0.04 g (20%). F{ H} NMR (188 MHz) d: 289.2 (4F, m,
2
1
:
Diisopropylamine (80 mL) was added to a mixture of
4
PyF), 2133.5 (4F, s, ArF), 2136.5 (4F, m, PyF). IR/cm
-ethynylpyridine (0.37g, 3.60 mmol), 1,4-diiodobenzene
0.51 g, 1.55 mmol), PdCl (PPh ) (0.018 g, 0.026 mmol) and
12 2
2229. HRMS (EI1): calc. for C20F N m/z 495.986987 found
495.987234.
(
2
3 2
CuI (0.005 g, 0.026 mmol). The reaction mixture was stirred
for 2 h after which the solvent was removed in vacuo. The
residue was dissolved in toluene and eluted through a column
of alumina (4 cm). Removal of the toluene gave the desired
Synthesis of 9,10-bis(4’-pyridylethynyl)anthracene (2) from 9,10-
diiodoanthracene
1
Diisopropylamine (40 mL) was added to a Schlenk flask
containing degassed mixture of 4-ethynylpyridine (0.09 g,
0.84 mmol) 9,10-diiodoanthracene (0.17 g, 0.40 mmol),
compound as a white powder. Yield 0.26 g (60%). H NMR
(
(
200 MHz) d: 7.39 (4H, m, PyH), 7.56 (4H, s, ArH), 8.63
2
4H, m, PyH). IR/cm : 2220. MS (M1): m/z 280. Anal. calc.
1
PdCl
2 3 2
(PPh ) (0.005 g, 0.008 mmol) and CuI (0.0015 g,
for C H N : C 85.69, H 4.31, N 9.99. Found: C 85.21, H 4.25,
2
0
12
2
0.008 mmol). The reaction mixture was stirred overnight
after which the solvent was removed in vacuo. The residue was
dissolved in hexane/ethyl acetate and eluted through a column
N 9.93%.
Synthesis of 1,4-bis(4’-pyridylethynyl)tetrafluorobenzene (1b)
1
of alumina (4 cm). Yield 0.09 g (63%). H NMR (200 MHz) d:
7.63 (4H, d, J ~ 6 Hz, PyH), 7.71 (4H, m, ArH), 8.66 (4H, m,
Triethylamine (60 mL) was added to a degassed mixture
of 4-ethynylpyridine (0.31 g, 3.00 mmol), 1,4-diiodotetra-
fluorobenzene (0.505 g, 1.25 mmol), PdCl (PPh ) (0.0175 g,
2
1
PyH), 8.73 (4H, d, J ~ 6 Hz, PyH). IR/cm : 2205. HRMS
1
17 2
(ESI: M 1 1 ): calc. for C28H N m/z 381.1392 found
2
3 2
0
.025 mmol) and CuI (0.0046 g, 0.025 mmol). The reaction
381.1413.
mixture was heated to reflux for 4 h after which the solvent was
removed in vacuo. The residue was dissolved in hot toluene and
eluted through a column of alumina (4 cm). Cooling of the
toluene solution gave the desired compound as pale yellow
Synthesis of 9,10-bis(4’-pyridylethynyl)anthracene (2) from 9,10-
dibromoanthracene
1
Triethyamine (40 mL) was added to a Schlenk flask containing
a degassed mixture of 4-ethynylpyridine (0.40 g, 3.88 mmol)
9,10-dibromoanthracene (0.49 g, 1.46 mmol), and CuI (0.011 g,
crystals. Yield 0.27 g (61%). H NMR (200 MHz) d: 7.46 (4H,
1
9
m, PyH), 8.69 (4H, m, PyH). F{ H} NMR (188 MHz) d:
1
2
1
2
132 (4F, s). IR/cm : 2227. MS (M1): m/z 352. Anal. calc.
for C20 : C 68.18, H 2.27, N 7.95. Found: C 68.21, H
.33, N 7.86%.
0
.057 mmol). In a nitrogen-filled glove-box, tri-tert-butyl-
phosphine (0.023 g, 0.114 mmol) was added to Pd(PhCN) Cl
0.022 g, 0.057 mmol) in dry, degassed toluene (1 mL). This
8 4 2
H F N
2
2
2
(
solution was removed from the glove-box and added to the
reaction mixture which was then stirred at room temperature
for 24 h, after which the solvent was removed in vacuo. The
residue was dissolved in hexane/ethyl acetate and eluted
through a column of alumina (4 cm). Yield: 0.39 g (70%).
Synthesis of 1,4-bis(2’,3’,5’,6’-tetrafluoropyridylethynyl)benzene
1c)
(
A solution of 4-bromo-2,3,5,6-tetrafluoropyridine (0.69 g,
.00 mmol) in triethylamine (20 mL) was added to a suspension
3
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 3 9 5 – 2 4 0 4
2 4 0 1

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Synthesis of 4-(pentafluorophenylethynyl)pyridine (3a)
X-Ray diffraction
Dry triethylamine (100 mL) was added to a flask containing
Crystals of 1b and 1c were grown by slow cooling of hot toluene
solutions, those of 2, 3a and 3b by slow evaporation of ethyl
acetate/hexane, hexane/DCM and hexane solutions, respec-
tively. The X-ray diffraction experiment for 1b was carried out
on a 4-circle Rigaku AFC6S diffractometer with a point
detector, using graphite-monochromated Cu-Ka radiation.
Reflection intensities were measured in 2h/v scan mode and
Pd(PPh
-ethynylpyridine (0.40 g, 4.0 mmol). Iodopentafluorobenzene
1.20 g, 4.0 mmol) was added and the reaction mixture was
3 2 2
) Cl (0.03 g, 0.04 mmol), CuI (0.01 g, 0.04 mmol), and
4
(
stirred at reflux for 6 h. The solvent was removed in vacuo, and
the residue was dissolved in diethyl ether and eluted through a
3
8
cm alumina column, and recrystallised from petroleum ether
0/100 to give the product as an off-white solid. Yield 0.40 g
2
5
integrated using teXsan software.
1
(
45%). Mp 123–124 uC. H NMR (200 MHz) d: 8.65 (2H, m,
The experiments for 1c, 2, 3a and 3b were carried out on
Bruker 3-circle diffractometers with SMART 6K (for 1c) or
SMART 1K (for 2, 3a, 3b) CCD area detectors, using graphite-
monochromated sealed-tube Mo-Ka radiation. The experi-
ment for 4 was carried out on a Bruker 3-circle diffractometer
with a ProteumM (APEX) CCD area detector, using graphite-
monochromated Mo-Ka radiation from a 60 W Mo-target
1
9
1
PyH), 7.42 (2H, m, PyH). F{ H} NMR (188 MHz) d: 2135.5
2F, m, PhF), 2151.0 (1F, m, PhF), 2161.5 (2F, m, PhF).
Anal. calc. for C13 N: C 58.01, H 1.50, N 5.20. Found: C
8.12, H 1.48, N 5.25%.
(
4 5
H F
5
Synthesis of 4-(phenylethynyl)tetrafluoropyridine (3b)
1
microfocus Bede Microsource X-ray generator with glass
A solution of n-butyllithium in hexanes (1.6 M, 6.25 mL,
1
acetylene (1.02 g, 10.0 mmol) in dry THF at 278 uC, and the
solution was stirred for 1 h. Pentafluoropyridine (1.69 g,
polycapillary X-ray optics. Full spheres of the reciprocal space
were scanned by several sets of narrow (0.3u) v scans, each set
with different (stationary) Q and 2h angles. The low tem-
perature of the crystals was maintained using Cryostream
0.0 mmol) was added dropwise to a solution of phenyl-
10.0 mmol) was added to the solution at 278 uC, and the
solution was allowed to warm to room temperature and stirred
(
intensities were integrated using the SAINT program.
Oxford Cryosystems) open-flow N
2
cryostats. Reflection
2
6
for 16 h. The solution was filtered through a column of silica
(
The structures were solved by direct methods and refined
2
by full-matrix least squares against F of all data, using
4 cm) using additional diethyl ether, and the filtrate was
2
7
evaporated. The residue was dissolved in hexane and eluted
through a silica column, and then recrystallised from hexane to
give the pure compound as white needles. Yield 2.23 g (89%).
SHELXTL software. All C, F and N atoms were refined in
anisotropic approximation, all H atoms in isotropic approxi-
mation. The crystal of 1c was a pseudo-merohedral twin, with
the components related by rotation around the [1 0 2] axis and
the reflections overlapping only partially. The intensity con-
tribution from the second crystal was estimated at 6.1(1)%. The
absolute configuration of 3b was not determined. Crystal data
and experimental details are listed in Table 4.
1
Mp 104–105 uC. H NMR (200 MHz) d: 7.63 (2H, m, PhH),
1
9
1
7
.46 (3H, m, PhH). F{ H} NMR (188 MHz) d: 290.9 (2F, m,
PyF), 2138.7 (2F, m, PyF). Anal. calc. for C13 N: C 62.16,
H 2.01, N 5.58. Found: C 62.35, H 2.04, N 5.47%.
5 4
H F
Synthesis of (4), the coordination polymer of (1b) with Zn(NO3)2
A solution of Zn(NO ?6H O (0.05 g, 0.17 mol) in ethanol
CCDC reference numbers 235646–235651.
See http://www.rsc.org/suppdata/jm/b4/b405128a/ for crys-
tallographic data in CIF or other electronic format.
3
)
2
2
(
0
10 mL) was carefully layered over a solution of 1b (0.01 g,
.028 mmol) in CH Cl (10 mL). After 10 d, light yellow
2
2
Differential thermal analysis (dta)
crystals suitable for X-ray diffraction were obtained at the
interface between the layers and a precipitate formed at the
bottom of the vial. After removal of a suitable crystal for
diffraction, the remaining sample was filtered and the solid was
washed with ethanol and CH Cl to remove any unreacted
A Mettler FP900 Thermosystem, consisting of a Mettler FP90
control processor linked to an FP84 sample hot stage, was used
to locate possible mesophase transitions in samples having
an approximate mass of 5 mg. The calorimeter was calibrated
with an indium standard. Experiments were conducted in an
2
2
starting materials. Yield 0.005g (45%).
Table 4 Crystallographic data and refinement parameters
Compound
1b
1c
2
3a
3b
4
Formula
Formula weight
T/K
Crystal system
Space group
C
352.28
150(2)
Monoclinic
P2 /n (no. 14)
5.787(1)
10.556(1)
13.112(1)
90
102.58(1)
90
781.7(2)
2
1.497
1.54178
1.06
150
1927
1542
20
H
8
F
4
N
2
C
424.25
110(2)
Monoclinic
P2 /c (no. 14)
8.920(2)
5.060(1)
18.101(4)
90
91.93(3)
90
816.5(3)
2
1.726
0.71073
0.17
60
10667
2373
20
H
4
F
8
N
2
C
380.43
160(2)
Monoclinic
C2/c (no. 15)
11.045(1)
23.945(3)
7.248(1)
90
96.940(3)
90
1902.8(4)
4
1.328
0.71073
0.08
56.6
5808
2176
28
H
16
N
2
C
13
H
4
F
5
N
C
251.18
120(2)
Orthorhombic
P2 (no. 19)
5.031(1)
8.831(3)
23.579(7)
90
90
90
1047.7(6)
4
1.591
0.71073
0.14
13
H
5
F
4
N
C
20 8 4 4 6
H F N O Zn
269.17
120(2)
Triclinic
541.67
120(2)
Monoclinic
P2/c (no. 13)
11.732(1)
5.274(1)
16.526(2)
90
96.428(5)
90
1016.0(2)
2
1.771
0.71073
1.29
58
7359
2702
0.019
2484
159
0.029
0.077
¯
1
1
P1 (no. 2)
5.834(2)
8.965(3)
11.009(4)
71.17(1)
82.05(1)
80.99(1)
535.9(2)
2
2
1 1
2
1
˚
a/A
˚
b/A
˚
c/A
a/u
b/u
c/u
3
˚
V/A
Z
23
rcalc./g cm
1.668
˚
l/A
m/mm
0.71073
0.16
61
7323
3206
0.053
1621
188
0.050
0.137
2
1
2hmax/u
58
Total reflections
Unique reflections
11716
1648
0.055
1548
183
R
int
0.018
1430
135
0.036
0.108
0.044
1679
144
0.067
0.254
0.026
1779
142
0.037
0.117
Reflections I w 2s(I)
Parameters
R [F, I w 2s(I)]
wR (F , all data)
0.037
0.084
2
2
4 0 2
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 3 9 5 – 2 4 0 4

View Article Online
environment of dry nitrogen, delivered through a cold finger at
C. Davis, D. Richardson and T. L. Groy, Acc. Chem. Res., 1998,
31, 474.
(a) A. J. Blake, N. R. Champness, P. Hubberstey, W. S. Li,
M. A. Witherby and M. Schroder, Coord. Chem. Rev., 1999, 183,
2
a flow rate of ca. 30 mL min . Thermographs were displayed
1
2
on a PC and analysed using Mettler FP99 system software
(
version 1). All heating and cooling operations were carried out
2
1
17; (b) N. L. Rosi, M. Eddaoudi, J. Kim, M. O’Keeffe and
1
at 10 uC min and the onset temperature was determined for
all transitions.
O. M. Yaghi, CrystEngComm, 2002, 4, 401; (c) B. Moulton and
M. J. Zaworotko, Curr. Opin. Solid State Mater. Sci., 2002, 6, 117;
(d) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter,
M. O’Keeffe and O. M. Yaghi, Science, 2002, 295, 469;
Prior to loading, the samples were crushed to a fine powder
using a mortar and pestle. Aluminium sample and reference
pans (25 mL) were hermetically sealed with aluminium lids
using a Perkin-Elmer press to give a cold weld capable of
withstanding pressures of up to 2 atm. Sample analysis was
conducted as follows: the pan containing the sample was
weighed and then placed in the appropriate compartment of
the dta; sample and reference pans were equilibrated at 50 uC;
(e) S. L. James, Chem. Soc. Rev., 2003, 32, 276.
3
(a) R. W. Gable, B. F. Hoskins and R. Robson, J. Chem. Soc.,
Chem. Commun., 1990, 1677; (b) S. Kawata, S. Kitagawa,
M. Kondo, L. Furuchi and M. Munakata, Angew. Chem., Int.
Ed. Engl., 1994, 33, 1759; (c) L. Carlucci, G. Ciani, D. M. Proserpio
and A. Sironi, J. Chem. Soc., Chem. Commun., 1994, 2755;
L. Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, J. Chem.
Soc., Dalton Trans., 1997, 1801; (d) O. M. Yaghi and H. Li, J. Am.
Chem. Soc., 1995, 117, 10401; (e) M. L. Hernandez,
M. G. Barandika, M. K. Urtiaga, R. Cortes, L. Lezama,
M. I. Arriortua and T. Rojo, J. Chem. Soc., Dalton Trans.,
2
1
both were heated, at 10 uC min , to at least 5 uC above the
sample’s clearing/degradation temperature and cooled to 50 uC
at the same rate before finally being returned to ambient tem-
perature; the sample pan was then re-weighed. This sequence
was carried out six times for each sample.
1
1
999, 1401; (f) M. A. S. Goher and F. A. Mautner, Polyhedron,
999, 18, 1805; (g) C. B. Aakeroy, A. M. Beatty and D. S. Leinen,
Angew. Chem., Int. Ed., 1999, 38, 1815; (h) L.-P. Zhang, W.-J. Lu
and T. C. W. Mak, Polyhedron, 2004, 23, 169.
(a) R. V. Slone, K. D. Benkstein, S. Belanger, J. T. Hupp,
I. A. Guzei and A. L. Rheingold, Coord. Chem. Rev., 1998, 171,
221; (b) T. Rajendran, B. Manimaran, F.-Y. Lee, G.-H. Lee,
S.-M. Peng, C. M. Wang and K.-L. Lu, Inorg. Chem., 2000, 39,
Transmitted polarised light microscopy (tplm)
4
An Olympus BH-2 transmitted polarised light microscope was
used to examine the phase transitions detected by differential
thermal methods. A Linkam THMS 600 heating/freezing stage
and TP 92 temperature programmer/controller were used to
enable observation of sample microstructures in situ at elevated
temperatures.
2
8
016; (c) S. S. Sun and A. J. Lees, J. Am. Chem. Soc., 2000, 122,
956; (d) C. Janiak, Dalton Trans., 2003, 2781.
5
6
(a) M. Fujita and K. Ogura, Coord. Chem. Rev., 1996, 148, 249;
(b) P. J. Hagrman, D. Hagrman and J. Zubieta, Angew. Chem., Int.
Ed., 1999, 38, 2638.
(a) X.-M. Chen, M.-M. Tong, Y.-J. Luo and Z.-N. Chen, Aust.
J. Chem., 1996, 49, 835; (b) J. Lu, T. Paliwala, S. C. Linn, C. Yu,
T. Niu and A. J. Jacobson, Inorg. Chem., 1997, 36, 923;
The microscopy procedure for identifying phase transitions
was as follows: samples in powder form were held between
BDH borosilicate coverslips (22 mm 6 22 mm; thickness no.1).
The glass was first cleaned by immersing in concentrated nitric
acid for 1 h, followed by thorough rinses in de-ionised water
and then acetone. Following this, the clean coverslips were
air-dried under a dust cover. Heating and cooling rates of
(c) A. J. Blake, S. J. Hill, P. Hubberstey and W.-S. Li, J. Chem.
Soc., Dalton Trans., 1997, 913; (d) M.-M. Tong, X.-M. Chen,
X.-L Yu and T. C. W. Mak, J. Chem. Soc., Dalton Trans., 1998, 5;
(e) M.-L. Tong, B.-H. Ye, J.-W. Cai, X.-M. Chen and S. W. Ng,
Inorg. Chem., 1998, 37, 2645; (f) K. Biradha, K. V. Domasevitch,
B. Moulton, C. Seward and M. J. Zaworotko, Chem. Commun.,
2
1
1
0 uC min were typical and a dry nitrogen purge was pro-
21
vided through the sample chamber at ca. 30 mL min in an
attempt to limit sample oxidation. In the case of compound 1b,
1
999, 1327; (g) S.-L. Noro, M. Kondo, T. Ishii, S. Kitagawa and
H. Matsuzaka, J. Chem. Soc., Dalton Trans., 1999, 1569;
h) S. A. Barnett and N. R. Champness, Coord. Chem. Rev.,
003, 246, 145.
2
1
heating rates of 0.5 uC min were employed to resolve a crystal
to crystal B/hexatic B transition, the phase transformation of
which was also estimated from this run.
(
2
7
(a) A. J. Blake, N. R. Champness, A. Khlobystov,
D. A. Lemenovskii, W. S. Li and M. Schroder, Chem.
Commun., 1997, 2027; (b) L. Carlucci, G. Ciani and
D. M. Proserpio, Chem. Commun., 1999, 449; L. Carlucci,
G. Ciani and D. M. Proserpio, J. Chem. Soc., Dalton Trans.,
1999, 1799; (c) K. Biradha and M. Fujita, J. Chem. Soc., Dalton
Trans., 2000, 3805; (d) A. J. Blake, G. Baum, N. R. Champness,
S. S. M. Chung, P. A. Cooke, D. Fenske, A. Khlobystov,
D. A. Lemenovskii, W. S. Li and M. Schroder, J. Chem. Soc.,
Dalton Trans., 2000, 4285; (e) M. B. Zaman, M. D. Smith and
H. C. zur Loye, Chem. Commun., 2001, 2256; (f) T. Rajendran,
B. Manimaran, R.-t. Liao, T. Ren-Jay, P. Thanasekaran,
G.-H. Lee, S.-M. Peng, Y.-H. Liu, I. Chang, S. Rajagopal and
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Acknowledgements
We thank NSERC (Canada) for funding (T. B. M.), and
EPSRC (UK) for studentships (J. C. C., A. J. S.) and a Senior
Research Fellowship (J. A. K. H.). T. M. F. thanks the Royal
Society (UK) for a Developing World Study Visit grant.
T. B. M. thanks the University of Durham for a Sir Derman
Christopherson Foundation Fellowship, and Johnson Matthey
plc for a loan of palladium chloride used in the Sonogashira
cross-coupling reactions. T. B. M. and J. A. K. H. acknowledge
One NorthEast for research support under the Nanotech-
nology UIC programme. We are grateful to Heriot-Watt
University for supporting S. W. W. through the award of a
studentship. We thank Ms. Jaroslava Dostal for performing
the elemental analyses, Ms. Lara Turner and Dr. Mike Jones
for performing the high resolution mass spectroscopy, and
Mr. Douglas Carswell for additional DSC measurements.
5
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